A detainee in the Prince George's County jail was injured yesterday when he was attacked by seven gang members in a holding area as they waited to be transferred to court for hearings, authorities said.

The assailants are thought to be members of the Bloods gang, a jail supervisor said. The gang has been a significant presence in the jail, and violence associated with it has grown in recent years, said the supervisor, speaking on the condition of anonymity because he is not authorized to speak publicly.

The victim, identified as a member of the Blackstone gang, was attacked sometime after 7 a.m., the supervisor said. Corrections officers, including members of an emergency response team, arrived quickly and quelled the violence, he said.

The detainee who was attacked was taken to a hospital for treatment, then to the jail's medical ward, said Vicki D. Duncan, a spokeswoman for the county Department of Corrections.

He was slightly injured, Duncan said, and no one else was reported wounded.

The seven gang members were taken to a disciplinary unit, and corrections officials are investigating the motive for the attack, Duncan said.

The victim might have been injured more seriously if fewer people had attacked him, the supervisor said. "All of them were trying to hit him at the same time, that's what saved him," he said.

It did not appear that any specific incident prompted the attack, the source said. "Bloods were marking their territory," he said.

The incident occurred a day after correctional officers told the County Council that the jail is increasingly violent and is so crowded that it is not possible to fully lock down the facility. The Upper Marlboro facility, which has 1,332 beds, housed an average of 1,482 inmates a day during the past fiscal year.

Leaders of the union representing county correctional officers told the council that officers are ill-equipped and under-trained and that the jail badly needs renovations.

Joseph Green, a lobbyist working on behalf of the union, said yesterday's incident highlights the problems that have been identified.

"This was just another day at the jail," he said. "It just gives more light to what they were talking about."